Sunday 23 October 2011 11.16 EDT
First published on Sunday 23 October 2011 11.16 EDT

Bangkok was preparing for more flooding on Sunday after the Thai prime minister warned that authorities were racing against time to protect the city. "Water is coming from different places, and headed in the same direction. We're trying to build walls but there will be some impact on Bangkok," Yingluck Shinawatra said.

Thailand has had its worst floods for half a century after months of unusually heavy rainfall, with 356 people killed since late July and more than 110,000 forced to move to shelters. About 2.5 million people have been affected, with water covering an area the size of Kuwait.

The disaster has been a tough start for the prime minister, a political novice elected in a bitter contest this summer. Opponents have accused the government of indecision and mismanagement.

Yingluck urged residents to move possessions at least a metre above the ground. In some parts of the city, water levels have already reached double that height.

On Saturday she said it could be six weeks before the waters subside. The situation is likely to be complicated by high tides due next weekend.

The floods first hit northern and central areas of the country, but torrents of water are now draining south, threatening the capital.

Yingluck has already ordered the opening of the city's floodgates in the hope that it would allow the waters to drain away through urban canals and into the sea. Officials feared that otherwise the defences would be overwhelmed.

Many have also complained about vague, confusing or contradictory information, which has left them uncertain about what to do. The government's supporters have said it is wary of panicking residents.

The Chao Phraya river reached its highest level for seven years on Saturday, but justice minister Pracha Promnok, who is heading the flood response team, said people should not worry too much because the overflow had been drained off.

He added that water in Klong Prapa, a canal that had been overflowing, was receding, and that water was also draining through other channels as planned.

Other reports suggested water levels continued to rise in parts of the canal.

Sean Boonpracong, the international spokesman for the flood response team, said food supply centres in or just outside Bangkok, meant to aid other parts of the country, had been hit by rising waters.

With residents anxious about supplies, many supermarkets in the capital have sold out of tinned food, instant noodles, bottled water and other essentials. Others began rationing goods.

Despite flooding in the Don Muang area, the city's second airport there has now become an evacuation base and a minister said it would also be used to supply food and water to residents.

Elsewhere in Bangkok, troops worked to fortify two key industrial zones, hoping to contain the economic damage wreaked by the disaster. According to the MCOT news site, the Thai chamber of commerce estimates that the floods have already cost the economy 400bn baht (£8bn). That would rise by another 120bn baht a month if business areas were flooded.

The governor of the central bank has said growth in south-east Asia's second largest economy could fall to 3% or less this year, rather than the 4.1% previously forecast. The finance minister has said it could even drop below 2%.

Seven industrial estates in Pathum Thani, Nonthaburi and Ayutthaya provinces have already halted production, with Toyota, Honda, Canon and Nikon among the companies affected. At least 600,000 people are unemployed due to the flooding. The labour ministry said that each would receive 2,000 baht.

The public health minister said he had ordered hospitals in areas of the city prone to flooding to evacuate critically ill patients to unaffected provinces.